[bio] cells Flashcards
what is a cell?
a basic unit of structure and function. it is the simplest unit with all characteristics of life
what are phospholipids?
a major component of biological membranes
special thing about phospholipids in cell membranes?
made up of two layers of phospholipids - phospholipid bilayer
why is phospholipid bilayer?
phospholipid tail is hydrophobic, needs the hydrophilic head to be facing outwards in contact with the extra cellular fluid outside the phospholipid bilayer
why is the cell membrane fluid
phospholipids and proteins are not stationary but can move rapidly across the surface of the membrane
why is the cell membrane mosaic
many different protein molecules are randomly scattered and embedded throughout the phospholipid bilayer
why are cell membranes partially permeable?
due to the nature of the phospholipids, only small hydrophobic molecules can pass through the phospholipid bilayer. as such, for hydrophilic or water-soluble molecules are unable to pass through the cell membrane, transport proteins are required.
what do you mean by partially permeable?
cell membrane only allows certain substances to pass through it
functions of partially permeable cell membrane
it functions to separate and protects a cell from its surrounding environment and controls how substances move in and out of the cell
what does cytoplasm contain
- cytosol
- cytoskeleton
- organelles
what is cytosol?
aqueous solution of essential ions, soluble proteins and soluble organic compounds such as sugars and amino acids
what is cytoskeleton?
network of protein fibres that give support, motility and regulation to the cell
what is organelles?
structures with specialised functions, suspended in the cytosol
what is cytoplasmic streaming
the movement of the fluid substance within a plant or animal cell
how does cytoplasmic streaming help?
aids in the transport of materials and organelles around the cell
structure of nucleus
largest organelle within the eukaryotic cell, usually spherical
what does the nucleus contains
- nuclear envelope
- nucleolus
- dna
what does nuclear envelope do
separates nucleus from the cytoplasm
what does nucleolus do
synthesise ribosomes
where are nucleus found
in almost all eukaryotic cells, except matured red blood cells
function of nucleus
- contains the hereditary material (dna)
- controls activities of the cell
structure of rough endoplasmic reticulum
a system of flattened membrane-bound sacs
how does it look under the microscope
appears “rough” under electron microscope because of the presence of ribosomes on its surface
functions of rer
protein synthesis - polypeptide chain synthesised by the ribosomes will be folded in the rer
structure of ser
consists of fine tubules
function of ser
- lipid synthesis
- detoxification of drugs and poisons
- storage and release of calcium ions
structure of Golgi apparatus
consist of stacks of flattened membrane-bound sacs
function of Golgi apparatus
chemically modifies products receive from the er and packages them, before sending them to destinations inside or out of the cell using vesicles
structure of lysosomes
small, spherical vesicles surrounded by a single membrane
what does lysosomes contain
hydrolysis enzymes such as lipases, proteases and nucleases
functions of lysosomes
- to digest materials made in the cell or take in from outside by phagocytosis (e.g. food vacuoles in Amoeba)
- to digest worn-out organelles in the cell, a process known as autophagy
structure of animal vacuoles
fluid-filled sac bound by a single membrane
how are animal vacuoles formed?
either by the pinching-off part of the cell membrane
or by enlargement of a vesicle from the Golgi apparatus
shape and size of animal vacuole?
usually relatively smaller and exists temporarily
function of animal vacuoles?
food vacuoles: formed by phagocytosis. in the case of intracellular digestion by macrophages
structure of plant vacuoles
enclosed by single, partially permeable membrane called the tonoplast
where is plant vacuoles found?
in mature plant cells, the large central vacuole is permanent and occupy over 80% of the cell volume
what is in the plant vacuole?
filled with cell sap, a solution of dissolved such as sugars, ions, waste products, and pigments
function of plant vacuole
- storage of nutrients such as protein storage in seeds and inorganic ions, e.g. K+ and Cl-
- disposal sites for metabolic by-products that would endanger the cell if they accumulated in the cytosol
- may contain pigment that colour the cell, e.g. red and blue pigments of petals to attract pollinators
structure of mitochondria
rod-shaped or cylindrical, bounded by double membrane
where is mitochondria found?
in plant and animal cells
function of mtiochondria
- involved in aerobic respiration
- contains DNA
- ATP is the “energy molecule” in living organisms
where is mitochondria found abundant in?
metabolically active cells
- e.g. muscle and liver cells
structure of chloroplast
bounded by a double membrane
what does chloroplast contain?
- chlorophyll
- thylakoids and stroma
function of chloroplast
site of photosynthesis
structure of ribosomes
small, round structures found in all cells
special thing about ribosomes?
may occur as free ribosomes suspended in the cytosol or bound to rough er
functions of ribosome?
- site of polypeptide synthesis
- free ribosomes generally make proteins that will function within the cytosol
- bound ribosomes generally make protein that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or for export from the cell
strucute of centrioles
small, hollow cylinders that occur in pairs
where are centrioles found?
in animals cells only, not in plant cells
function of centrioles
play a role in cell division in animal cells
similarities of animal and plant cells
both contain:
- cell membrane
- mtiochondria
- nucleus
- cytoplasm
differences between plant and animal cell
chloroplast:
- plant: chloroplasts are present in large number of photosynthetic cells
- animals: chloroplast are absent
centrioles:
- plant: centrioples are absent
- animals: centrioles are present
vacuole:
- plant: present as a single, large and central vacuole
- animal: vacuoles are small and numerous
